A woman brings flowers to commemorate the recently murdered child in Moscow on March 1, 2016. (REUTERS/Sergei Karpukhin)

A horrific incident in Moscow, in which a woman was apprehended brandishing the severed head of a child and screaming that she would blow herself up, has shaken a city already on a high alert for a possible terrorist attack.

Passers-by had captured footage of the 38-year-old woman holding the infant’s head high in the air and screaming “I am a terrorist, I want your death,” before being wrestled to the ground by police outside a subway station on Monday, Reuters reports. Investigators said they thought the woman, from the former Soviet republic of Uzbekistan, had been working as a nanny for a Moscow family, and had murdered a child under her care before setting fire to the family’s apartment. The child was 3 or 4 years old, they said.

“Given the clearly deranged behavior of the detainee, investigators swiftly ordered her to undergo psychiatric tests to establish whether she is capable of understanding the significance of her actions,” Moscow’s investigative committee said in a statement.

Lifenews.ru — a news portal with close contacts among law enforcement authorities — reported that the hijab-wearing woman had been approached near the metro station by a police officer, requesting to see her identity papers, before she removed the child’s head from a bag, shouting and threatening to blow herself up. The police officer was assisted by colleagues in restraining her.

Rights activists expressed concern at a possible backlash against migrant workers from Central Asia by far-right agitants, as a result of the day’s events. The Associated Press reported that the story had not carried been carried on any of the main Russian TV channels, although president Vladimir Putin’s spokesman denied on Tuesday that the news had been withheld at the request of the Kremlin or out of concerns over racial tension being stoked in a country with a large Muslim population.

This is a disgrace. Where is the UK foreign office in all of this? Aras Amiri now joins another British-Iranian, Nazanin Zaghari-Ratcliffe, in notorious Evin prison on bogus charges. @foreignofficehttps://t.co/DJX0knhdot